The present invention relates to a bottom dead center correction device for a servo press machine, in which a slide is raised and lowered with a servo motor as the power source. The present invention is effective for correcting the bottom dead center in one micron units for each stroke of the slide using a detector sensor provided on a die of the machine for detecting bottom dead center measurement value.
It also provides bottom dead center correction is conducted in response to fluctuations in the molding load due to deformations resulting from heat in the construction arts of the servo press or die or due to unevenness in the hardness of the material to be processed.
A servo press machine drives the servo motor so that the bottom dead center of a stroke of the vertical motion of the slide has, as the bottom dead center command value, a bottom dead center setting value which has been set at a control device. The bottom dead center of the slide stroke is maintained at a constant. A bottom dead center detection value is detected by a position detection device, which detects the position of the slide. In addition, by having feedback of the bottom dead center detection value, there is a correction per stroke. Fluctuations in the bottom dead center resulting from distortions of frame parts due to pressure from molding and deformations due to heat generated during rotation and sliding are corrected.
In the prior art, for example, Japanese Laid-Open Patent Number 6-218594 corrects the distortion amount of the frame.
In the above described technology of the prior art, a test molding is conducted when setting the bottom dead center, and the setting value for the bottom dead center is determined from the precision of the molded product. In later moldings, the fluctuation of the bottom dead center due to distortion of frame parts and deformation due to heat generation of moving parts is detected by a slide position detection device. Because correction is conducted to match the detected value with the setting value, the precision of the bottom dead center can be made to 5-10 microns.
However, the slide position detection device detects the position of the slide, but does not measure the actual bottom dead center of the die. If there is any fluctuation in the actual bottom dead center of the die due to a load and the like during the molding, there is no method for correction. There is no way of having a correction that can achieve a bottom dead center precision greater than that described above.
In a known device, the fluctuations of the bottom dead center due to deformations of the construction members as a result of molding load and as a result of heat are corrected, and the distance between the upper surface of the bed or bolster and the lower surface of the slide is measured directly with a linear scale, and the height fluctuation amount is continuously being corrected.
In another prior device, corrections not only of the fluctuations of the bottom dead center due to deformation of the construction parts of the servo press, but also fluctuations due to deformation of the die are made. For example, the touch point at which the punch of the upper mold contacts the processing material, which is supplied onto the lower mold, is detected. At the time of detection, the distance from the bed or bolster upper surface to the slide lower surface is measured. The fluctuation amount of the distance is continually being corrected. According to this device, there can be corrections in response to changes in the thickness of the processing material.
In the above described prior art, with the former method, in which there is correction for the fluctuations of the bottom dead center due to deformations of the construction parts of the servo press or the die resulting from molding force or heat, the bottom dead center precision is maintained at 5-10 microns.
Furthermore, with the latter method, in which in addition to the former method, there is correction for fluctuations of the bottom dead center due to changes in the thickness of the processing material, the bottom dead center precision can be improved by a few microns.
However, there still remains the problem of correcting fluctuations of the bottom dead center arising from fluctuations in the molding load due to variability in the hardness of the processing material. In general, a coil material is used for the processing material. However, even if the coil material is manufactured under conditions in which the thickness and hardness are adequately maintained, the beginning, middle, and end of the coil may not be consistent. The following improvements are still needed: preventing fluctuations in the molding amount resulting from fluctuations in hardness; improving the bottom dead center precision from the 5-10 microns of the prior art; and improving the product precision.
An object of the present invention is to solve the above problems and to provide a bottom dead center correction device for a servo press machine which can conduct corrections based on a bottom dead center actual measurement value detected from a bottom dead center detection sensor provided on the die during molding, and which can correct at a bottom dead center precision of 1 micron units.
In a first embodiment of the invention, a bottom dead center correction device for a servo press machine, being a bottom dead center correction device for a servo press machine which has a servo motor as its drive source and controls the vertical linear motion of a slide based on a set top dead center position and a bottom dead center position of the slide, wherein: the bottom dead center position of the slide is corrected by a bottom dead center measurement value detected from at least one bottom dead center detection sensor provided on a die.
In the bottom dead center correction device, the temperature drift of the bottom dead center detection sensor is corrected based on temperature rise value of the die detected by a temperature sensor provided on the die. Furthermore, in order to verify a detection precision of the bottom dead center detection sensor, a detection value from a position detection device, which detects the position of the slide, and an output value from the bottom dead center detection sensor are compared, and failure of the bottom dead center detection sensor can be determined.
Another object of the invention is to provide a device for bottom dead center correction by the load of the servo press. The bottom dead center correction device can correct the bottom dead center fluctuations due to deformation of the construction parts of the servo press and the die resulting from variability in the hardness of the processing material.
In a second embodiment of the invention, a device for correcting a bottom dead center by detecting a molding load in a servo press is provided. The servo press has a servo motor with numerical control as a drive source and provides a slide with a raising and lowering motion. With this embodiment, there is provided: a scale detection device, which detects the distance between a bed or bolster upper surface and a slide lower surface (henceforth referred to as xe2x80x9cslide positionxe2x80x9d) and which outputs an electrical position signal; a current detection device, which detects a current value which is supplied to the servo motor and corresponds to the load value of the slide; and an NC control device, which controls a rise and fall motion of the slide by controlling the current value that is supplied to the servo motor so that it corresponds to a pre-set slide motion.
In addition, when one or the other of either the slide load value, which is calculated from a current value inputted from the current detection device, or a slide position, which is inputted from the scale detection device, reaches a set value, the NC control device corrects the set bottom dead center of the slide according to the difference between the other value and its set value.
In this bottom dead center correction device, when the slide load value, which is calculated by the NC control device, reaches a pre-set value, if the slide position, which is outputted from the scale detection device, is higher than a pre-set position, the processing material is determined to have a high hardness, and the set bottom dead center of the slide is corrected downward by the amount of the correction value, and the slide is lowered. Conversely, if the position is lower than the pre-set position, the processing material is determined to have a low hardness, and the set bottom dead center of the slide is corrected upward by the amount of the correction value, and the slide is lowered.
On the other hand, when a slide position, which is outputted from the scale detection device, reaches a pre-set slide position, if the load value, which is calculated by the NC control device, is larger than a pre-set load value, the processing material is determined to have a high hardness, and the set bottom dead center of the slide is corrected downward by the amount of the correction value, and the slide is lowered. Conversely, if the load value is lower than the pre-set load value, the processing material is determined to have a low hardness, and the set bottom dead center of the slide is corrected upward by the amount of the correction value, and the slide is lowered.
Furthermore, a touch point, which is where an upper mold which is lowered together with the slide contacts a processing material supplied onto a lower mold, is detected by a rise in the current value outputted from the current detection device. When the touch point is detected, the corrected value for the set bottom dead center of the slide obtained from an output of the scale detection device can be corrected. In other words, the set bottom dead center of the slide can be corrected in response to changes in the thickness of the processing material.
The above, and other objects, features and advantages of the present invention will become apparent from the following description read in conjunction with the accompanying drawings, in which like reference numerals designate the same elements.